Journal
IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS
Volume 2, Issue 3, Pages 231-244Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TBCAS.2008.2003199
Keywords
Action potential; biomedical circuits; blocking-capacitor; capacitance reduction; current generator; fail-safe; functional electrical stimulation (FES); implanted device; neural stimulator
Funding
- European Commission under IMANE [IST-026602]
- Engineering and Physical Sciences Research Council [EP/F009593/1] Funding Source: researchfish
- EPSRC [EP/F009593/1] Funding Source: UKRI
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We present a neural stimulator chip with an output stage (electrode driving circuit) that is fail-safe under single-fault conditions without the need for off-chip blocking-capacitors. To miniaturize the stimulator output stage two novel techniques are introduced. The first technique is a new current generator circuit reducing to a single step the translation of the digital input bits into the stimulus current, thus minimizing silicon area and power consumption compared to previous works. The current generator uses voltage-controlled resistors implemented by MOS transistors in the deep triode region. The second technique is a new stimulator output stage circuit with blocking-capacitor safety protection using a high-frequency current-switching (HFCS) technique. Unlike conventional stimulator output stage circuits for implantable functional electrical stimulation (FES) systems which require blocking-capacitors in the microfarad range, our proposed approach allows capacitance reduction to the picofarad range, thus the blocking-capacitors can be integrated on-chip. The prototype four-channel neural stimulator chip was fabricated in XFAB's 1-mu m silicon-on-insulator CMOS technology and can operate from a power supply between 5-18 V. The stimulus current is generated by active charging and passive discharging. We obtained recordings of action potentials and a strength-duration curve from the sciatic nerve of a frog with the stimulator chip which demonstrate the HFCS technique. The average power consumption for a typical 1-mA 20-Hz single-channel stimulation using a book electrode, is 200 mu W from a 6 V power supply. The silicon area occupation is 0.38 mm(2) per channel.
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